#1.添加字段ALTER TABLE student ADD stuAge INT NOT NULL;#2.修改字段ALTER TABLE student CHANGE stuAge sAge VARCHAR (100)NOT NULL;#3.修改表名ALTER TABLE students RENAME student;#4.删除字段ALTER TABLE student DROP sAge;#1.添加唯一约束ALTER TABLE grade ADD CONSTRAINT stuName UNIQUE KEY(stuName);#2.删除唯一约束ALTER TABLE gradeDROP INDEX stuName;#1.添加默认值约束 (地址默认北京)ALTER TABLE studentALTER COLUMN stuAddress SET DEFAULT ‘北京‘#2.删除默认值约束ALTER TABLE studentALTER COLUMN stuAddress DROP DEFAULT#1.给student表中添加一个stuAge的字段ALTER TABLE student ADD stuAge INT #2.给stuAge添加一个检查约束，验证是否可以成功ALTER TABLE student ADD CONSTRAINT ck_stuAge CHECK (stuAge>=18)#3.验证stuAge字段的检查约束是否成功INSERT INTO student(stuName,stuGradeid,stuAge)VALUES("陈七",1,17)#4.删除检查约束是不成功的ALTER TABLE studentDROP CONSTRAINT ck_stuAge#1.删除外键约束ALTER TABLE student2DROP FOREIGN KEY FK_Grade_Student_GradeId#ALTER TABLE student2 ADD CONSTRAINT FK_Grade_Student_GradeId FOREIGN KEY (stuGradeid) REFERENCES `grade`(gid)